Simultaneous saccharification and fermentation of alkali-pretreated cogongrass for bioethanol production

Abstract

Simultaneous saccharification and fermentation (SSF) of alkaline pretreated cogongrass to ethanol was optimized using the commercial cellulase Accellerase 1500 and Ethanol Red dry yeast. Cogongrass was pretreated with 10% (wt) NaOH at room temperature for 24 hours, resulting in an increase in the cellulose percentage from 38.5% to 60.5%. Each SSF of alkali-pretreated cogongrass was carried out with 1 g/L of dry yeast loading at pH 5.0 under 150 rpm shaking. Response surface methodology (RSM) based on a three-level three-factor Box-Behnken design was employed to optimize the key variables within the following ranges: cellulase concentration per unit gram water-insoluble cellulose (WIS) (0.15-0.25 mL/g-WIS), substrate concentration (5-15 % WIS, w/w), and temperature (35-45°C) for the SSF process. The response surface model arrived at the optimum SSF conditions: cellulase concentration of 0.255 ml/g-WIS, temperature at 37.5°C, and substrate concentration of 7.28% WIS for obtaining 80.3 % ethanol yield in 72 h. The optimal conditions were verified experimentally with an average absolute relative deviation of 3.01 %. Also, the SSF was scaled up to a 5-L rotary drum reactor filled with 1 kg of substrate under the optimal conditions, and an ethanol yield of 76.2% was obtained.